In a projection type image magnifying apparatus (including projection type television receiver), in order to reduce the size of the housing of the apparatus, a method is proposed to install a mirror between the video light emission source (for example, liquid crystal projector) and the projecting screen, and reflect the image by the mirror to project on the screen (see FIG. 7).
As the mirror, hitherto, a glass mirror, or a mirror having a reflecting film forming a reflecting surface mounted on a metal frame by using an adhesive has been used.
The glass mirror, especially a face side mirror (the mirror not allowing the light to pass through the glass which is the support member of the reflecting surface is called a face side mirror) is excellent in smoothness, durability and reflection characteristics, but has a defect of high risk of breakage and is heavy. For example, in the case of a glass mirror used in a 43-inch projection type image magnifying apparatus, the size is 869 mm by 583 mm, and the total weight is over 4 kg including the reinforcing panel for mounting. Hence it does not contribute to reduction of weight and cost of the set.
On the other hand, in the case of a mirror in a reflecting film adhered structure (hereinafter called a film mirror), the weight is about 1 kg in the same size, and the weight is reduced, and it is increasingly used in the projection type image magnifying apparatus.
FIG. 14 shows an example of a configuration of optical parts in a liquid crystal projection type image magnifying apparatus. In FIG. 14, a projection line is projected from a liquid crystal projector 50 using a liquid crystal panel, and reflected by a mirror 49, and a projected image 56 is focused on a screen 48.
However, when a conventional film mirror is used in the mirror 49 as in FIG. 14, the projected image 56 on the screen 48 may be colored, or is separated into rainbow colors.
A sectional view of a reflecting film used in a conventional film mirror is shown in FIG. 11. The reflecting film used in a conventional film mirror is composed of a transparent film 43, on which a metal thin film 42 is evaporated, and the metal surface of the transparent film side is used as the reflecting surface (this mirror is called a back side mirror because the light transmits through the film 43 which is a support member of the reflecting surface). On the opposite side of the transparent film 43 side of the metal thin film 42, a metal thin film of high weather resistance is formed, or a resin-made protective film 41 is formed. That is, the front surface of the metal thin film 42 is a transparent film 43 as the base, and projective means 41 for assuring weather resistance or the like is provided on the rear surface.
In this constitution, an incident light 44 enters the transparent film 43, and is reflected by the metal thin film, and the reflected light 45 passes again through the transparent film 43 and exits.
Herein, problems of light separation and coloring occur in the process of the projected light entering the transparent film, being reflected by the metal surface, and passing again through the transparent film to exit. The reason is discussed below.
FIG. 12 shows an orientation state of a material of transparent film as the base in the prior art. For the transparent film material as the base, as shown in FIG. 12, a wide and long polyester film 46 or the like is used. This polyester film 46 is usually exposed to stretching, more or less, in the manufacturing process of the polyester film 46. As a result, high molecules in the film produce an orientation 47 in the longitudinal direction and width direction of the film. By the orientation of high molecules formed in the film, the film comes to have an anisotropy of rays for causing birefringence of rays. In the case of reflection through a birefringent substance, the reflection is complicated. Birefringence is known to differ in the refractive index of abnormal light when the incident direction is different. In addition, depending on the wavelength of the incident light, the refractive index differs.
Therefore, in the prior art, in the process of passing through the transparent film, entering polarized light, reflecting on the reflecting surface, and leaving from the transparent film, the axis of polarization of the incident polarized light rotates. The situation differs with color. It moreover differs depending on the incident angle and direction to the mirror.
FIG. 13 shows a configuration of electronic parts of a liquid crystal projection type image magnifying apparatus in the prior art. In FIG. 13, the image delivered from a liquid crystal projector 50 is projected by a liquid crystal projector projecting lens 51, reflected by a mirror 49, and magnified and projected on a screen 48. The ray of light passing through the liquid crystal panel and projected from the projector is polarized, either p polarized light or s polarized light.
The ray of light converged on one spot on the screen is the polarized light emitted from the liquid crystal projector being reflected in a wide range of the mirror.
Therefore, when the transparent film stretched in the manufacturing process is used as the film mirror for receiving and reflecting the ray of light in the liquid crystal projector, the imaging on the screen is a synthesis of polarized lights for producing the axes of polarization mutually different in a wide range of mirror, which is a synthesis of complicated images differing in each color.
This is considered because the projected image 56 on the screen 48 is colored, or separated into rainbow colors. In the case of a film mirror as disclosed in Japanese Laid-open Patent No. 4-339642, it is a back side mirror using the ordinary PET film side as mirror, and the above problems occur. As a result, color deviation may occur on the screen, rainbow colors may appear, moire stripes may be formed, or double images or multiple images may be formed.
Moreover, the light is reflected not only on the metal thin film, but also on the PET film surface. Still more, since the PET film has an important role as a support member, it cannot be made too thin, and hence the image appears to be double or multiple images, and the picture quality deteriorates.
Therefore, the conventional film mirror is not suited to the reflecting mirror for liquid crystal projection type image magnifying apparatus.
On the other hand, when using the face side mirror not allowing the light to pass through the film used as the support member of the reflecting surface, the demerits of the back side mirror are eliminated, but when the reflecting surface of the metal thin film is exposed, metal is oxidized, and the reflectivity is lowered, and it gives rise to requirement of protective film of the reflecting surface of the metal thin film, and when a protective film having anisotropy of ray was used as its protective film, the above problems occurred. Besides, development of protective film excellent in weather resistance has been demanded.